A variety of implantable medical devices (IMDs) for delivering a therapy, monitoring a physiological condition of a patient or a combination thereof have been clinically implanted or proposed for clinical implantation in patients. IMDs may deliver therapy to or monitor conditions of a variety of organs, nerves, muscle or tissue, such as the heart, brain, stomach, spinal cord, pelvic floor, or the like. The IMDs may employ stimulation electrodes, sense electrodes, and/or other sensors carried by one or more elongated electrical leads or within or along the housing of the IMD.
Some IMDs, such as cardiac pacemakers or implantable cardioverter defibrillators (ICDs), provide therapeutic electrical stimulation to or monitor the heart of the patient. The electrical stimulation provided by the IMD may include signals such as pacing pulses, cardioversion shocks or defibrillation shocks to address abnormal cardiac rhythms such as bradycardia, tachycardia or fibrillation.
In some cases, the IMD senses signals representative of intrinsic depolarizations of the heart and analyzes the sensed signals to identify normal or abnormal cardiac rhythms. Upon detection of an abnormal rhythm, the device may deliver an appropriate electrical stimulation signal or signals to restore or maintain a more normal rhythm. For example, an IMD may deliver pacing pulses to the heart upon detecting tachycardia or bradycardia or deliver cardioversion or defibrillation shocks to the heart upon detecting tachycardia or fibrillation.
More than one IMD may be implanted in a patient based on individual patient need. More than one IMD may be required for monitoring conditions that may require a therapy and for delivering different types of therapies. In some cases, more than one IMD may be required to monitor cardiac signals and deliver therapies to different chambers of the heart, or more generally monitor physiological signals and deliver therapy at various sites in the patient's body.